A power inverter, or an inverter, or a DC-to-AC converter, is an electronic device or circuitry that changes direct current (DC) to alternating current (AC) (e.g. single- and/or 3-phase).
A power inverter would typically be a switching inverter that uses a switching device (solid-state or mechanical) to change DC to AC. There are may be many different power circuit topologies and control strategies used in inverter designs. Different design approaches address various issues that may be more or less important depending on the way that the inverter is intended to be used. For example, an inverter may use an H bridge that is built with four switches (solid-state or mechanical), that enables a voltage to be applied across a load in either direction.
Given a particular power circuit topology, an appropriate control strategy may need to be chosen in order to meet the desired inverter specifications, e.g. in terms of input and output voltages, AC and switching frequencies, output power and power density, power quality, efficiency, cost, and so on.
For example, one of the most obvious approaches to increase power density would be to increase the frequency that the inverter operates at (“switching frequency”). This may be done by employing wide-bandgap (WBG) semiconductors that use materials such as gallium nitride (GaN) or silicon carbide (SiC) and can function at higher power loads and frequencies, allowing for smaller, more energy-efficient devices.
A typical way to control a switching inverter is by mathematically defining voltage and/or current relations at different switching states to produce the “desired” output, obtaining the appropriate digitally sampled voltage and/or current values, then using numerical signal processing tools to implement an appropriate algorithm to control the switches [1]. However, such a straightforward approach often calls for performance compromises based on the ability to accurately define the voltage and current relations for various topological stages and load conditions (e.g. nonlinear loads), and to account for nonidealities and time variances of the components (since the values of, e.g., resistances, capacitances, inductances, switches' behavior, etc., may change in time due to the temperature changes, mechanical stress/vibrations, aging, etc.). In addition, a control processor for the inverter must meet a number of real-time processing challenges, especially at high switching frequencies, in order to effectively execute the algorithms required for efficient DC/AC conversion and circuit protection. Various design and implementation compromises are often made in order to overcome these challenges, and those can negatively impact the complexity, reliability, cost, and performance of the inverter.
Thus there is a need in a simple analog (i.e. continuous and real-time) controller that would allow us to bypass the detailed analysis of various topological stages during a switching cycle altogether, thus avoiding the pitfalls and limitations of straightforward digital techniques.
Further, there is a need in such a simple controller that (i) does not require any current sensors, or additional start-up and management means, (ii) provides robust, high quality (e.g. low voltage and current harmonic distortions), and well regulated AC outputs for a wide range of power factor loads, including highly nonlinear loads, and also (iii) offers multiple ways to optimize the cost-size-weight-performance tradespace.